1. Field of the Invention
This invention relates to an electrochemical device having a multilayer structure and methods for making such a device. Specifically, this invention relates to a multilayer electrochemical device having nano-sized conductive agents and/or active materials within polymer layers.
2. Description of the Related Art
Cobalt oxyhydroxide (CoOOH) has been used in the nickel electrode of NiCd and NiMH batteries as an electronic conductor (Pralong, Delahyaye-Vidal, et al., 2000). Cobalt hydroxide [Co(OH)2] is currently added to the nickel hydroxide paste to prepare the nickel composite electrode used in nickel based rechargeable alkaline batteries. Cobalt incorporation into the active mass of the nickel oxide electrode is usually realized either by chemical substitution of nickel during the Ni(OH)2 synthesis (e.g., co-precipitation) or by separate addition of cobalted component, namely, cobalt-based salts.
Benson et al. studied the electrochemical behavior of cobalt compounds in alkaline medium and their results showed a poor performance of electrochemical reversibility for cobalt hydroxide/oxyhydroxide (Benson, Briggs, et al., 1964). Butel et al. studied the electrochemical behavior of CoOOH prepared from a ceramic precursor Na0.6CoO2. The results from Butel et al. show the presence of an electronically conductive β′-CoOOHx containing small amounts of Co+4 (Butel, Gautier, et al., 1999). Butel et al. further found that a voltage reduction of this β′ phase down to 0.92V [vs. Cd/Cd(OH)2] led to a stoichiometric phase of β-CoOOH which is not so conductive. The results from Butel et al. are consistent with the observations in Pralong et al.
Generally, carbon is added in lithium ion batteries to provide conductivity. However, carbon is usually combustible. Therefore, there are disadvantages when using carbon conductive agents, especially for commercial applications such as aircraft.
Thus, needed in the art are electrochemical devices having nano-sized conductive agents and/or active materials that are less combustible and that can be prepared using an in situ method and process. It would be of great significance that the electrochemical devices can be produced at room temperature and no carbon conductive agents are needed for increasing conductivity of the electrochemical devices.